In modern machine tool operations, especially for precision machining, boring, removal of material utilizing a cutting tool, it is common practice after a machining operation to measure the workpiece and adjust the position of the tool in accordance with the measurement, i.e. so as to compensate for any dislocation of the tool from its planned position based upon the programming of the machine.
While this generally does not pose a problem where the workpiece is rotated and the tool is stationary, e.g. in external turning on a lathe or the like, since the energy necessary to adjust the position of the tool can be applied to the latter without concern for the rotation of the spindle, and hence electrical, pneumatic and hydraulic means have been provided for adjusting the tool in the past, when the tool is rotated, e.g. in a boring machine, adjustment of the tool position relative to a tool carrier which is received in the machine spindle poses a problem.
In a boring machine, the workpiece may be held stationary and the tool, in this case a boring bar, is chucked or otherwise received in the tool spindle and may comprise a tool bit which has a cutting edge projecting laterally from the boring bar.
In such cases the use of energy carriers for electrical, pneumatic or hydraulic control of the position of the cutting edge relative to the tool carrier is problematical because of the rotation of the tool.
In machine tools of the CNC (Computer Numerical Control or direct numerical control) type wherein the tool can be automatically changed, for example by drawing new tools from a tool magazine by a so-called tool changer, and inserted into the spindle in the course of machine operation, the ability to adjust the position of the tool bit has proved to be especially important. Upon the termination of a cutting operation, the tool is withdrawn by the tool changer from the spindle and returned to the magazine.
In Speed Automatic Sizing (SAS) systems for numerical control machine tools, the spindle with a tool in place is brought into a defined starting position and, utilizing a steeping motor, the position of the tool bit relative to the tool carrier, i.e. the portion of the tool received in the spindle, can be adjusted.
Such adjustment does not usually involve an absolute shift in the tool bit relative to the carrier but may be a result of a measurement after each cut or after several cuts and is generally an adjustment by a relative amount depending upon the results of the measurement.
Systems of this type utilizing a stepping motor are expensive, massive in size and occupy valuable space in the working region. In addition, they are generally electrically controlled so that complex control systems are required and complications are introduced by the need to deliver electrical energy to the stepping motor.